Pivotable spherical joints, commonly referred to as ball joints, generally include a ball stud engaged in a socket. Such joints have a wide variety of applications where a pivotable connection between two parts is desirable. For example, they may be used in many types of linear actuators and have been found to be particularly useful in automotive lamp assemblies. As seen in U.S. Pat. No. 5,707,133 the disclosure of which is incorporated herein by reference, automotive lamp assemblies used as headlights typically comprise several basic parts: a support frame, a reflector, a lens, a bulb, and one or more adjusters.
In the automotive lamp assembly example, the support frame houses the reflector and the bulb on a pivotable mounting to allow the aim of the light to be adjusted using the adjuster. The lens seals the front of the assembly to protect it from the elements assailing the front end of the vehicle and provides an aerodynamic shape and attractive appearance. Typically, the reflector mounts inside the housing on one fixed ball joint and is adjustable horizontally and vertically using adjusters that interface with the reflector through moving ball joints. The moving ball joints are moveable by actuating the adjusters connected to the moving ball joints by a ball stud having a head and a shaft. Another type of automotive headlamp assembly that uses linear actuators is shown in U.S. Pat. No. 5,360,282. In this type of headlamp assembly the linear actuator is mounted to a bracket and the ball joint end supports a reflector, lens and light bulbs. This type of application requires a higher strength ball joint due to the additional weight being supported. In particular, pull-out strength of the ball joint needs to be greater to withstand vibration.
While one possible application of the present invention is in headlamp assemblies, other applications are possible and references to use in a headlamp assembly should not be deemed to limit the application of the present invention. Additionally, while the improved ball socket design described herein may be designed for use with a disengageable ball stud, such as those described in U.S. Pat. Nos. 6,113,301; 6,247,868; and 6,758,622, the disclosures of which are incorporated by reference, it can also be used advantageously with ball studs having “ears” or engaging tabs or semi-spherical ball stud designs. Examples of such adjusters are disclosed in U.S. Pat. Nos. 4,689,725; 5,186,531; and 6,758,622. One additional benefit of the ball joint of the present invention is that it eliminates the variances associated with using semi-spherical ball studs, resulting in consistent pull out resistance.
Conventional ball joints for use in automotive lamp assemblies typically include a ball stud with a spherical engagement head extending from an adjuster. The ball stud is moveable linearly in and out of the adjuster. While generally effective, there are a number of shortcomings to using a ball stud in a conventional socket that includes a plurality of resilient tabs to retain the ball stud. One such shortcoming is that the tabs typically contact the ball stud sphere up to or on a “tangent point” that is on an imaginary line between the pivot center of the ball stud and the center of the resilient tab, e.g., the configuration shown in U.S. Pat. No. 6,758,622. This configuration causes the force generated when the stud is subjected to pull-out force, to be directed along the imaginary line. This configuration results in a condition where the ball stud may be pulled out of socket under certain conditions of operation, such as vibration while supporting heavier reflectors or in heavier headlamp assemblies like the one previously referenced in U.S. Pat. No. 5,360,282, leaving the adjuster non-operational. This unexpected pull-out generally occurs because the retention tabs are necessarily flexible to allow the head to be installed in the socket. Though pull-out of the ball stud is resisted to some degree of success, if enough pull-out force is applied, the tabs deflect and the ball stud head slips through and “pops out.” Reducing the flexibility of tabs is not a desirable option because it would either be too difficult to insert the ball stud head into socket, or the elasticity of the tabs would be lessened to the degree that they would break off during insertion of the ball stud.
While steel ball studs, particularly those with an undercut behind the head of the ball stud or ears that engage tabs or other structure can achieve high pull-out force resistance, it is often preferred to use a plastic ball stud to enable the use of more compact and light weight adjuster designs. Further, plastic ball studs can be designed that have undercuts behind the heads, tabs or other retaining structure, but for manufacturing, installation, and design flexibility, a full round ball stud head is generally preferred.
Accordingly, the need exists for an improved ball socket that securely retains a ball stud placed therein, can be effectively used in connection with disengageable or conventional ball studs, can be effectively used with plastic ball studs, is cost effective, and has greater resistance to accidental pull-out.